Method of printing



May 31, 1966 K. G. LUSHER 3,253,540

METHOD OF PRINTING Filged April 19, 1963 5 Sheets-Sheet l ,QTTQRNEYS May31, 1966 K. G. LUSHER 3,253,540

METHOD OF PRINTING 'Filed April 19, 1965 5 Sheets-Sheet 2 INVENTOR.KENNETH G. LuHE/zl ,ClrroRA/EVS May 31, 1966 K. G. I UsHl-:R

METHOD OF' PRINTING 5 Sheets-Sheet Z Filed April 19, 1963 1 N VENTOR,/fEN/VErH G. LujHE/z United States Patent O The present inventionrelates to a method of printing and more particularly to a method offorming a printing image for transfer to a surface to be printed.

In my copending, earlier Ifiled application Serial No. 242,229, filedDecember 4, 1962, now Patent No. 3,150,- 547, and in the earlier filedapplication of William H.

- Wood, Serial No. 242,230, yfiled December 4, 1962, both of saidapplications being assigned to the assignee of the instant invention,there have been disclosed various methods for the formation of an imageto be printed upon a surface, the image being formed of printingparticles transferred to the surface to be printed (preferably byelectrostatic means), and cured thereon in any desired manner, such asby heating, vapor fusing, covering with a transparent coating, or thelike.

As particularly disclosed in my own above-identified application, theparticles are formed to the image to be printed by a silk screen processwherein the particles are superimposed upon and brushed or otherwiseforced through a foraminous screen or the like onto an offset printingplate.

The present invention provides a method of image formation in which theprinting particles are adhered to the screen, rather than beingdisplaced therethrough.

More specifically, the present invention contemplates the utilization ofa foraminous carrier element, such as a silk screen or the like, havingan open image-defining pattern thereon. Conventional silk screeningprocesses may be utilized to -form the open image-defining pattern; eg.the pattern may be photographically developed on the screen utilizing aconventional photo-sensitive gelatin or the pattern may be pierced orchemically etched in a metallic sheet or foil. In any event, the termscreen is used generically herein to denote a foraminous carrier elementhaving openings corresponding to and defining, preferably inmirror-image form, the pattern to be printed.

The screen, after its formation, is provided with apertures which aresmaller than the particles to be printed. A plurality of randomlyoriented printed particles are formed into a gaseous suspension, e.g.air-floated, and are directed against the surface of the foraminousscreen by differential gaseous pressure. The gaseous medium, of course,passes freely through the screen, while the particles are screened outat the screen surface at locations corresponding to the location of thescreen apertures. The thickness of the resultant particle layers can beeasily regulated, e.g. by varying the concentration of the suspension,the suspension flow rate, or the time of exposure of the screen to thesuspension. By maintaining the differential gaseous pressure, theparticles are adhered to the screen surface until such time as they aretransferred to the surface to be printed.

In a preferred embodiment of the invention, the screen is positionedadjacent a body of randomly oriented printing medium particles in atray-like container, and a vacuum head or box is fitted to the screenand evacuated to create a vacuum at the screen openings. The pressuredifferential thus created between the screen and the supply body ofparticles will cause some of the particles `of the body to migratethrough the screen surface, Since the particles are larger than thescreen spacing, the particles will become adhered to the screen and willremain in place so long as the-vacuum is maintained. Thus, therePatented May 31, i966 is provided, at the screen surface, a plurality ofprinting particles oriented on the surface in accordance with theopenings therein dening the pattern to be printed.

IFinally, the screen or foraminous surface bearing the particles at theopenings therein is positioned adjacent the surface to be printed, andthe particles are transferred to the surface to `be' printed in the samepattern `and in the same orientation as the particles existed at thescreen. This transfer can be accomplished in several different ways,e.g. by electrically attracting the particles from the screen to thesurface to be printed, by blowing the particles onto the surface to beprinted, by contacting the particles with a heated surface to be printedso that the particles fuse to the surface, or in any other desiredmanner.

Additionally, multi-colored printing -can be accomplished by utilizingindividual screens for each of the colors to be printed and individuallytransferring particles .from the individual screens to a compositescreen, which serves as an offset medium from which the differentlycolored particles are transferred to the surface to be printed in any ofthe different ways set forth above.

It is, therefore, an important object 'of the present invention toprovide a new and improved method of printing utilizing printingparticles which are oriented into a desired pattern at a foraminousscreen by creating a pressure differential between a body of theparticles and the screen to transfer particles from the body to theScreen to define thereon the pattern to be printed.

Another important object of the present invention is to provide a methodof printing wherein a `body of randomly oriented printing mediumparticlesand a foraminous screen having openings corresponding to thepattern to be printed are superimposed and the screen is evacuated toattract to and adhere at the screen a layer of the particles, theparticle layer being subsequently transferred to and affixed on thearticle to be printed.

It is a still further object of this invention to provide a method offorming an image to be printed by transferring to and adhering at aforaminous transfer medium a pluarity of printing particles subjected toa pressure differential, maintaining the pressure differential whilesuperimposing the transfer medium on the article to be printed, and`finally transferring the particles to the surface to be printed.

Yet another, and no less important, object of this invention is theprovision of a method of making a multicolored image to be printed byattracting to and adhering at different foraminous surfaces theappropriately differently colored printing particles and sequentiallytransferring the differently colored particles to a common carrierelement by evacuating the carrier element.

Other objects of this invention will appear in the following descriptionand appended claims, reference being had to the accompanying drawingsforming a part of this specification wherein like reference charactersdesignate corresponding parts in the several views.

On the drawings:

FIGURE 1 is a diagrammatic representation of an initial step of thepresent invention, utilizing a foraminous screen fitted with a vacuumhead and superimposed over a body of printing particles;

FIGURE 2 is a view similar to FIGURE l illustrating the transfer of theprinting particles to the screen by air floatation of the particles;

FIGURE 3 is a view illustrating the transfer ofthe particles from thescreen to a surface to be printed by electrical means;

FIGURE 4 illustrates a modied method of the present invention wherein acontinuous foraminous screen is utilized and the printing particles aretr-ansferred from 3 the screen to the surface to be printed bymechanical pressure alone;

FIGURES 5 through 9 illustrate the method of the present invention asadapted to the formation of multicolored printing images simultaneouslytransferred elec'- trostatically to the article to be printed from acomposite offset image. v

Before explaining the present invention in detail, it 1s to beunderstood that the invention is not limited in its application to thedetails of construction and arrangement of parts illustrated in theaccompanying drawings, since the invention is capable of otherembodiments and of being practiced or carried out in various ways. Also,it is to be understood that the phraseology or terminology employedherein is for the purpose of description and not of limitation.

As shown on the drawings:

In FIGURE 1, reference numeral refers generally to a foraminous carrierelement comprising a screen 11 formed of Woven stainless steel wire orthe like mounted in a surrounding, perimetric frame 12. Applied to thescreen 11 is a conventional gelatin coating 13.

As explained in my earlier led applications, such screens are generallyreferred to as silk screens, although the screen element thereof may beformed of fine wire, such as stainless steel wire, or by punching,etching or otherwise forming small apertures in a metallic plate or thelike. The screen 11 is coated with and invested within the non-metalliccoating 13 which is substantially thicker than the thickness of the wire11 and which is generally va gelatinous material, such as a bichromatedgelatin applied to the metallic screen 11 as a solution and allowed todry in the absence of light. The dried gelatinous rnaterial is sensitiveto light, and the gelatin will become insoluble in water upon exposureto light. The light sensitive resultant screen 10 may have imagesreadily reproduced thereon by various well known photographictechniques. In that embodiment of the invention illustrated in FIGURE lof the drawings, it will be seen that the screen 10 is provided with amedial, coating-free aperture 15.

In air-tight contact with the frame 12 of the screen 10 is a vacuum headindicated generally at 16 and having an interior air passage 17connected to a suitable source of vacuum or reduced pressure, theevacuation of the space 17 being illustrated by the directional arrow18. The evacuation of the space 17 encompassed by the head 16 will, ofcourse, induce a current of air through the opening in the screen 10.

The screen 10 is superimposed over an open-topped tray or container 20containing a supply of particulate printing medium 21 of the typedescribed in my earlier iled application. Several specific particlecompositions are disclosed in my earlier filed application and theearlier filed application of William H. Wood (both of which areabove-identified), and it is unnecessary to repeat these compositions inthe instant application.

However, it will be appreciated that the particle size of theparticulate material 21 in the container 20 is greater than the openingsof the Wire 11. Thus, by way of example, particles of the type andcomposition set forth in my earlier led application having a particlesize of from 13 to 26 microns can be utilized in conjunction with a 325by 325 mesh screen 11.

As illustrated in FIGURE 2 of the drawings, the continued evacuation ofthe space 17 will induce a draft of air upwardly through the screenopening 15 and particles from the container 20 will be air-floatedupwardly against the undersurface of the screen to be deposited thereonin a layer indicated at 25. The air in which the particles are dispersedwill pass freely into the vacuum head 16, while the particles will bescreened out at the aperture 15. So long as the vacuum indicated by thedirectional arrow 18 is maintained, the layer 25 of the particles willremain in place. Further, it has been found that the longer the vacuumis maintained and the relative positions of the supply of particles 21and the screen remains fixed, the thicker `the layer 25 will become. Byvarying the degree of evacuation of the vacuum head 16 and by varyingthe length of time that the relationship of FIG- URES 1 and 2 ismaintained, the various thicknesses of particles can be built up on theundersurface of the screen 10.

After the desired layer 25 of particles has been built up upon theundersurface of the screen 10, the screen 10 and the container 20 arerelatively moved, and the screen is positioned adjacent'a surface 30 tobe printed. f

Where the surface being printed is non-conductive, e.g. a paper surface,the surface may be backed up by a conductive metallic plate 31 connectedto one side of a high voltage source, as by lead line 32, the other sideof the high voltage source, either A.C. or D.C.,.being connected by leadline 33 to the metallic screen 11. By applying a relatively highvoltage, e.g. on the order of 200 to 20,000v

volts, across the space between the screen 11 and the conductive plate31, the particle layer 25 adhered to the undersurface of the screen bythe vacuum 18 will be transferred to and deposited upon the interposedsurface 30 to be printed.

The electrical transfer of the particle layer 25 to the surface 30 is,of course, due to the fact that the particles at the screen 11 will pickup the charge of the screen and will be transferred to the surface 30 byvirtue of the relative opposite polarity of the conductive plate 31.Depending upon the actual operating conditions, the vacuum 18 may bemaintained during the electrostatic transfer, in which case theelectrostatic attraction must be greater than the differential pressureurging the particles against the screen 11, or the vacuum may beinterrupted during the electrostatic transfer. Subsequent to theirtransfer to the surface of the article 30, the particles are adheredthereto by techniques well known in the art, as above explained.

In that embodiment of the invention illustrated in FIG- URE 4 of thedrawings, an endless, belt-type foraminous element 40 is utilized, thisbelt having openings therethrough defining the pattern or a mirror imageof the pattern to be printed. The belt 40 is trained about a pair ofguide rolls 41, 42, one of which is driven, to provide a lower effectivehorizontal reach 43 underlying a vacuum head 4S of the type heretoforedescribed and evacuated as indicated by the directional arrow 46. Thevacuum head 45 is continuously evacuated and serves to transfer to theundersurface of the reach 43 of the belt 40 printing particles from asupply 47 of such particles in a container or tray 48. The particlesadhered to the undersurface of the belt reach 43 are indicated`generally at 49, such particles being oriented in conformity to thepattern of openings in the belt reach 43.

The surface to be printed preferably constitutes a web 50 trained abouta pair of rolls 51 and traveling in the same direction as the belt reach43, i.e. in the direction of directional arrows 53. The web 50 to beprinted is heated to a temperature less than its kindling point bysuitable means, as by a fuel fired burner emitting a llame 56 contactingthat surface of the web 50 which is subsequently moved into facingrelationships to the undersurface of the reach 43 of the belt 40.

The location of the upper roll 51 is such that the web 50 is in pressurecontact with the particles 49 adhered to the undersurface of the web 43and the vacuum head 45 is of such size and configuration that at thetime of initial contact between the web 50 and the belt reach 43 theparticles 49 are still subjected to the inuence of the vacuum indicatedby the directional arrows 46.

Thus, the vacuum head 45 serves to adhere particles 49 from the supply47 of such particles on the undersurface of the foraminous belt 40 andserves to retain these particles on the belt until, and preferablyafter, pressure contact exists between the particles 49 and the web orsurface 50 to be printed. Since the web 50 is heated, as by the burner55, the pressure and heat of contact between the particles 49 and theweb 50 will effectively transfer the particles to the web 50.

In that embodiment of the invention illustrated in FIG- URES 5 through9, substantially the same operations as performed in FIGURES 1 through 3are repeated for different colors or particles.

More particularly, in FIGURE 5 of the drawings, the screen indicatedgenerally at 60 is conveXo-concave in configuration and is secured to avacuum head 61 which is evacuated, as at 62, so that particles 63 from acontainer 64 are adhered to the open portions of the screen surface, asat 65. Subsequently, the vacuum head 61 and the screen 60 bearing theadherent particles 65 are positioned immediately adjacent a secondscreen 66 carried by a separate Vacuum head 67, the screen 66 beingconcavo-conveX and of matching configuration to the screen 60 after thescreens 60, 66 are juxtaposed, as illustrated in FIGURE 6, the vacuum inthe head 61 is released and a Vacuum is applied to the head 67, asindicated by directional arrow 68 to transfer the particles 65 from thescreen 60 to the screen 66. The screen 66 has openings 69 registeringwith the openings 65 in the screen 60 and additional nonregisteringopenings 70 therein.

A third screen 71 having a different aperture pattern therein defined byopenings 76 and provided with a vacuum head 72 is evacuated, asindicated at 73, to transfer particles 74 of a different coloration froma different container 75 to the screen 71, as at 76. Preferably, theparticles transferred to the screen 71, as at 76, are of a differentcoloration than the particles applied to the screen 60. After transferof the particles from the screen 60 to the screen 66, the screen 60 isremoved from its position over the screen 66, and the screen 71 ispositioned in juxtaposition to the screen 66, as illustrated in FIG- URE8. Upon now interrupting the vacuum in the vacuum head 72 whileretaining the vacuum in the vacuum head 67, the particles 76 aretransferred from the screen 71 to the screen 66.

Thus, the screen 66, of concavo-convex configuration, is provided withlayers of particles 65 and 76 of different coloration. Finally, thescreen 66 bearing the two different colors of particles is positionedadjacent the article to be printed, i.e. a glass container of generallycylindrical configuration, indicated generally at 80. By heating thesurface of the glass article 80 to an elevated temperature (as disclosedin the above-identified application of William H. Wood) and impressing ahigh volta-ge on the screen 66 and the surface of the article 80, thedifferently colored particles 65, 76 can be readily electricallytransferred at the same time to the surface to be printed.

Thus, the embodiment of the invention illustrated in FIGURES 5 through 9provides a means for separately forming partial images of differentcoloration (at screens 6 60, 71), transferring these partial images to acomposite screen 66 to form a complete multi-color image, and thenconcurrently imposing the multi-color image particles from the screen 66onto the article 80.

I claim:

1. In a method of printing utilizing a particulate printing medium, thesteps of superimposing separate supplies of randomly oriented printingmedium particles of distinct coloration and separate foraminous screenswith apertured masks to define different open patterns thereon,respectively, creating a vacuum at each said open screen pattern toattract to and adhere at said screen a layer of said particles from thecorresponding supply of particles, thus forming a plurality ofdifferently colored partial pattern layers at the separate screens,sequentially transferring the partial pattern layers in registry witheach other to a single composite evacuated screen masked to define thecomplete pattern in a layer upon said composite screen, and finallytransferring said complete pattern layer from said composite screen to asurface to be printed.

2. In a method of printing a desired multi-colored imageutilizingprinting medium particles of different colors, the steps ofsuperimposing upon separate supplies of randomly oriented printingmedium particles of distinct coloration a plurality of separateforaminous screens each having an apertured mask to define differentopen patterns thereon corresponding, respectively, to different portionsof the image to be printed, creating a vacuum at each said open `screenpattern to attract to and adhere at said screen a layer of particlesfrom the corresponding supply of particles, thus forming a plurality ofdifferently colored partial pattern layers on the separate screens,separately l transferring the individual partial pattern layers to asingle composite evacuated screen in Iregistry with each other to definethe complete multicolor pattern to be printed, and finally electricallytransferring said complete multicolored pattern from said compositescreen to a surface to form said desired multicolor image upon saidsurface.

lll

References Cited by the Examiner UNITED STATES PATENTS 1,668,322 5/1928Kessler 101-116 X 2,239,619 4/1941 Murgatroyd et al. 101-129 X 2,525,13510/1950 Huff 210-404 2,590,321 3/1952 Huebner. 2,787,556 4/ 1957 Haas.3,093,039 6/ 1963 Rheinfrank.

ROBERT E. PULFREY, Primary Examiner'.

WILLIAM B. PENN, Examiner.

PAUL R. WOODS, Assistant Examiner.

1. IN A METHOD OF PRINTING UTILIZING A PARTICULATE PRINTING MEDIUM, THE STEPS OF SUPERIMPOSING SEPARATE SUPPLIES OF RANDOMLY ORIENTED PRINTING MEDIUM PARTICLES OF DISTINCT COLORATION AND SEPARATE FORAMINOUS SCREENS WITH APERTURED MASKS TO DEFINE DIFFERENT OPEN PATTERNS THEREON, RESPECTIVELY, CREATING A VACUUM AT EACH SAID OPEN SCREEN PATTERN TO ATTRACT TO AND ADHERE AT SAID SCREEN A LAYER OF SAID PARTICLES FROM THE CORRESPONDING SUPPLY OF PARTICLES, THUS FORMING A PLURALITY OF DIFFERENTLY COLORED PARTIAL PATTERN LAYERS AT THE SEPARATE SCREENS, SEQUENTIALLY TRANSFERRING THE PARTIAL PATTERN LAYERS IN REGISTRY WITH EACH OTHER TO A SINGLE COMPOSITE EVACUATED SCREEN MASKED TO DEFINE THE COMPLETE PATTERN IN A LAYER UPON SAID COMPOSITE SCREEN, AND FINALLY TRANSFERRING SAID COMPLETE PATTERN LAYER FROM SAID COMPOSITE SCREEN TO A SURFACE TO BE PRINTED. 